This invention relates to a cable hauling system and, more particularly, to a mechanical cable hauling system employing only an energy-dissipating, power transfer device to allow differential rotation between a haulback drum and a main drum.
In cable hauling systems normally used for yarding logs, cable is wound about a haulback drum. From the haulback drum, the cable threaded through an idler sheave on a boom and extends outwardly to an outhaul block at a location remote from the boom. The portion of the cable extending from the haulback drum to the outhaul block is referred to as the haulback line. The cable then extends from the outhaul block back toward the boom to a grapple carriage, a choker cable, or other mechanism for grasping and holding a log or turn of logs. From the carriage, the cable extends back to the boom, through another idler sheave and is wound about a second drum, normally referred to as a main drum. The portion of the cable extending from the outhaul block to the main drum is referred to as the main line.
In coventional cable hauling systems, positively acting clutches are employed to selectively engage either the main drum or the haulback drum to a drive shaft, depending upon whether the carriage is to be brought toward or away from the boom. When a clutch associated with one of the drums is engaged, the clutch associated with the other drum, generally referred to as the trailing drum, is disengaged. Large, energy-dissipating brakes are associated with the trailing drum to prevent it from free wheeling and thus to maintain tension in the cables. Such mechanical braking is satisfactory for intermediate sized systems and for some larger systems. For larger, high horsepower systems, however, brake wear is excessive, resulting in constant maintenance and replacement of brake linings. Moreover, for such systems, control over the speed of the haulback line and the main line during hauling and lowering and raising of the turn of logs can be imprecise, consequently requiring that an operator possess much experience to handle the system well and efficiently.
Another cable hauling system currently used is generally referred to as an interlocked system. In an interlocked system, the main drum and the haulback drum are usually driven from a common drive shaft and are either counterrotated or the cables are wound in opposite directions thereon to haul the carriage from the outhaul block to the boom and back again. During hauling of the carriage, the effective diameters of the main drum and haulback drum vary because the number of wraps of cable on each of the drums vary as line is wound onto and payed out from the drums. Assuming the two drums are driven at constant speeds, the varying effective diameters of the main drum and the haulback drum will cause a slackening or tightening of the main line and haulback line as the carriage is being hauled. The slackening or tightening of the main and haulback lines is compensated for in most interlocked systems by either a mechanical or hydraulic variable speed differential.
Both the mechanical and hydraulic interlocked systems are relatively expensive. Thus, they are uneconomical to employ in applications where only small cable hauling systems are required. Likewise, the use of two or more energy-dissipating, slipping brakes in the conventional systems is economically prohibitive because of the associated large initial costs and ongoing maintenance costs. Thus, none of the prior art systems is really suitable for the smaller logging operations where only one or a few logs are hauled at one time. Accordingly, it is a broad object of the present invention to provide a relatively inexpensive, relatively low maintenance, simple to operate cable hauling system, especially such a cable hauling system for use in yarding logs or transferring other loads from one point to another along a generally fixed path. Further objects of the present invention are to provide a relatively simple mechanical system that employs an energy-dissipating, power transfer device, but at the same time reduces wear and maintenance on the clutch parts; and to provide such a system in which the power transfer device functions to provide variable speed interlock between a main drum and haulback drum regardless of the rotational direction.